As Sen. Bernie Sanders (I-Vt.) looks to score a momentum-building victory in the Iowa caucuses just 10 days from now, the progressive populist is ramping up his attacks on rival Hillary Clinton for delivering paid speeches before Wall Street banks after leaving the State Department, seizing on Clinton's hefty fees to depict her as a creature of the financial establishment.

But Clinton is defending her decision to deliver the speeches, which often brought in upwards of $225,000 a pop.

"Anybody who thinks they can buy me doesn't know me," Clinton said in a Des Moines Registerinterview Thursday.

The former secretary of state added that she spoke "to so many different groups" after leaving the Obama administration in 2013.

"What they were interested in were my views on what was going on in the world. And whether you're in health care, or you sell automobiles, or you're in banking – there's a lot of interest in getting advice and views about what you think is happening in the world," she told the Register.

Sanders' attack: That defense won't mollify Sanders. The senator argues that Clinton's Wall Street speaking fees are evidence of a cozy relationship with the financial industry, which has helped bankroll her bids for the United States Senate and president.

"Goldman Sachs also provides very, very generous speaking fees to some unnamed candidates, very generous," the Register quoted Sanders as telling voters in Carroll, Iowa, on Wednesday. "Now I know that some of my opponents are very good speakers, very fine orators, smart people. But you gotta be really, really, really good to get $225,000 a speech. That's all I'll say."

As the New York Times noted, Clinton has received a total of $675,000 from Goldman Sachs for delivering three speeches. But progressive concern goes beyond the mere fact that Clinton raked in big bucks from 30-minute speeches before banks.

During some appearances, Clinton reportedly sounded decidedly less populist notes than she's been hitting on the campaign trail. The Times reported that during a $275,000 speech before GoldenTree Asset Management in 2013, Clinton defended the 2010 Dodd-Frank financial reform law but added that Wall Street should be seen as "a partner in securing the country's economic future, not an enemy."

Sanders, meanwhile, boasts that he'd be an enemy of Wall Street.

"The CEOs of large multinationals may like Hillary. They ain't going to like me — and Wall Street is going to like me even less," he said in last month's Democratic debate in Manchester, New Hampshire. "And the reason for that is we've got to deal with the elephant in the room, which is the greed, recklessness and illegal behavior on Wall Street."